Detonator device



1962 c. s. IRISH, JR

DETONATOR DEVICE Filed Sept. 22, 1958 FIG. 3

FIG-4 lgvous 5,0

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INVENTOR. CHARLES G. IRISH, JR.

VOLTAGE- CURRENT CURVE OF I N90 GERMANlUM DIODE United States Patent3,022,446 DETONATOR DEVICE Charles G. Irish, In, Cheshire, Conm,assignor to Olin Mathieson Chemical Corporation, a corporation ofVirginia Filed Sept. 22, 1958, Ser. No. 762,409 1 Claim. (Cl. 317-80)The present invention relates to electric detonators, blasting caps orsimilar devices and deals inparticular with a means for rendering thedevices responsive to a given level of electrical energy while beingnon-responsive to a lower energy level.

It is a particular feature of the invention to provide an electricaldetonator which functions at normal current levels but which requireshigh voltage for firing.

The range of normal current is intended to extend from .1 amp. to 20amps. while the language high voltage includes a range of from about 25volts to about 300 volts.

By virtue of the range of voltage levels at which the firing of devicesof the present invention are responsive or non-responsive, it ispossible to achieve selective detonation of a string or group ofdetonators by merely wiring a plurality of detonators together whereeach is actuated by a difierent voltage.

Thus, selective firing can be achieved by means of a variable voltagepower supply and appropriate time delays can be incorporated in such afiring plan readily.

A further feature of the invention is that the electrical detonator hasan exceedingly low probability of being fired by unwanted signals suchas electrostatic voltages or induced currents from electromagneticfields.

Another feature of the invention is the provision of an electricaldetonator whose electrical continuity may be tested safely by relativelyhigh voltages prior to activating the detonator. These test voltages mayrange from to 50 volts less than the firing voltage depending upon thevalue or magnitude of the desired firing voltage.

An electrical detonator embracing certain features of the presentinvention may comprise a housing or shell, an ignition assembly disposedwithin the shell comprising a pair of lead wires connected at theirterminals to a bridge wire and at least two germanium diodes in circuitwith the lead wires.

Other features and advantages of the present invention will become moreapparent from the succeeding specification when read in conjunction withthe appended drawings in which:

FIG. 1 is a perspective view of a detonator embracing the principles ofthe invention with certain portions of the housing broken away forclarity;

FIGS. 2 and 3 show preferred circuit arrangements, and,

FIG. 4 shows a typical voltage-current curve of a 1N9O germanium diode.

Referring now in detail to the drawings there is shown a detonatorindicated generally by the reference numeral 10 including a tubularhousing 11 enclosing at one end an appropriate priming charge 12 withinwhich there is disposed a bridge wire 13 connecting the terminals of apair of leads 14 and 16. The end of the housing from which the leadwires 14 and 16 protrude is appropriately sealed with waterproofingcompound such as asphalt, wax, epoxy resin or the like, as indicated bythe reference numetal 21.

Disposed within the sealed end of the tubular housing 11 is a smallboard or plate 17 formed of insulating material and snugly engaging theinterior diameter of the tube. Mounted upon the board 17 are twogermanium diodes 18 and 19. The diodes are electrically connected to theleads .14 and .16 in accordance with the wiring diagram of FIG. 3 sothat the diode 18 is in series with the lead 14 while the diode 19- isin series with the lead 16.

It is intended that these diodes possess a reasonably high value ofinitial resistance, for example, 67,000 ohms, with a correspondingdecrease in resistance, an inverse voltage characteristic, upondissipation of power in the diode. Diodes having the necessary inversevoltagecharacteristics include germanium gold-bonded diodes and pointcontact diodes. For example, point-contact diode 1 N has been foundsatisfactory.

An alternative scheme for arranging the circuit of the detonator isshown in FIG. 2 wherein two diodes are shown wired in series with thelead 14.

FIG. 4 shows in graphic form the electrical characteristics of a diodeutilized in the present invention. Note the inverse voltagecharacteristic wherein, initially, the current increases slightly withan increase in voltage; thereafter the voltage drops as currentcontinues to increase.

Thus, the present invention affords a means for convetting any standardelectric primer, detonator, match, squib blasting cap, etc. into anignition device which requires high firing voltages. Although thecurrent requirements remain normal, the power requirements are higherbecause of the higher voltages. The high voltage and power requirementsfor firing make it very difficult to fire by unwanted signals such aselectrostatic discharges or induced currents from electromagneticfields.

As stated previously, a preferred form of the invention would embrace astandard blasting cap with two 1N90 diodes back to back incorporatedinto the leads as shown in FIGS. 2 and 3. The blasting cap modified inthis manner can be checked for continuity with voltages up to 50 voltswith no danger of firing because current remains low as apparent in FIG.4. In prior art devices, any voltage source used to check continuitymust have a current limiting resistor.

In the detonator of the present invention the current at 50 volts willnot exceed 750 microamperes, while the current required to fire theordinary detonator is in excess of times as great.

A typical arrangement for operating my blasting cap involves connectingthe leads to a variable transformer which is, in turn, connected tovolts A.C. As the voltage is slowly raised, the current increases verylittle until the inverse voltage rating of the diode is approached (50to 60 volts for the 1N90). As the voltage exceeds this value the currentincreases because the power rating of the diode is exceeded. Eventuallythe dynamic resistance (represented by slope of curve of FIG. 4) of thediode goes to zero and the diode then enters a negative resistanceregion wherein the voltage across the diode drops and sizable currentsflow actuating the ignition device. The large currents usually destroythe two diodes by changing the conductivity of the germanium and bymelting the fine contact wire.

Two diode types have been found to be satisfactory. These are the pointcontact diode and the gold bonded diode. There are many diodes of bothtypes of structure with different characteristics. By selection ofproper diode, insensitivity to voltages ranging from 30 volts to 250volts can be obtained. The 1N90 has been selected because it providesadequate protection and is reasonably priced.

The variety of electrical characteristics available facilitates thedesign of a series of blasting caps which will fire at different voltagelevels--50, 75 and 100 volts, for example. In blasting operations thisfeature affords a decided advantage in that multiple banks of chargescould set off at any desired time interval.

Obviously, a variety of modifications and arrangements of the detonatorof the present invention can be devised without departing from thespirit and scope thereof.

diode; whereby said test voltage level is of the order of 15 to 50 voltslower than the firing voltage level, and the test current is about 750microamperes.

References Cited in the file of thispatent i a UNITED STATES PATENTS2,514,434 iWindes July 11, 1950 2,828,692 Webster Apr. 1, i958 2,909,122Shoemaker et al Oct. 20, 1959 FOREIGN PATENTS 320,243 Switzerland u---May 15, 1957

